To learn more about the antecedents and immediate precursors of sudden cardiovascular deaths and major disabling illnesses, we plan to complete the analysis of relevant data gathered during prospective studies of 1,196 American men aged 20 to 65 who have been followed from one to eighteen years with complete examinations and 6- to 24- hour tape recordings of their electrocardiograms. Our aim is to improve our estimates of risk; to detect immediate precursors of new events; to determine the antecedents of disorders of the cardiac conduction system; to study social data, behavor, high alcoholic intake and disorders of carbohydrate metabolism as antecedents of events; and to complete the development of our computer-assisted analysis of 24-hour tape recordings.